Medical imaging apparatus, program installable in medical imaging apparatus, and medical imaging method

ABSTRACT

A medical imaging apparatus includes a cardiac lumen region identifying unit, a myocardium identifying unit, and a generating unit. The cardiac lumen region identifying unit is configured to identify a cardiac lumen region from a medical image including a heart region. The myocardium identifying unit is configured to identify a face of a myocardium region obtained by extending a face of the cardiac lumen region, identified by the cardiac lumen region identifying unit, by a certain distance toward a myocardium side. The generating unit is configured to generate a color-coded image in which the face of the myocardium region, identified by the myocardium identifying unit, is colored in colors according to signal values of the medical image corresponding to positions on the face of the myocardium region.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a medical imaging apparatus, a programinstallable in a medical imaging apparatus, and a medical imagingmethod.

Description of the Related Art

Ischemic heart disease (IHD), which is caused by blocking the blood flowto myocardium due to obstruction or narrowing of coronary arteries,generally occurs in endocardium and progresses toward epicardium. Whenthe disease reaches epicardium, it may be difficult to cure the disease.It is thus significantly necessary to detect the disease in an earlystage. To this end, techniques for detecting narrowing of coronaryarteries in an early stage by using various medical image diagnosticapparatuses have been sought in recent years.

Japanese Patent Laid-Open No. 2013-10005 discloses a medical imagingapparatus capable of detecting the presence of a narrowing of coronaryarteries by obtaining a blood flow rate or the gradient of a blood flowrate in each region of coronary arteries, from a plurality of items ofvolume data captured at different times, which are obtained bycapturing, by an X-ray computed tomographic (CT) scanner, images of theheart of a patient (subject being tested) into which a radiocontrastagent has been injected, and by generating an image that represents theform of the coronary arteries colored in accordance with the level ofthe blood flow rate or the gradient of the blood flow rate.

However, the medical imaging technique disclosed in Japanese PatentLaid-Open No. 2013-10005 requires to obtain a plurality of items ofvolume data captured at different times by the CT scanner. Not only theamount of captured data becomes vast, but also the amount of thepatient's exposure to radiation becomes great. It is thus hard to saythat this is a simple image generating technique.

Research on diagnosis of ischemia in recent years has found that amechanical stress on myocardium causes an ischemic state to appear insystole. This shows the possibility that using a medical image capturedin such systole can contribute to early detection of ischemic heartdisease.

SUMMARY OF THE INVENTION

A medical imaging apparatus according to an embodiment of the presentinvention includes a cardiac lumen region identifying unit, a myocardiumidentifying unit, and a generating unit. The cardiac lumen regionidentifying unit is configured to identify a cardiac lumen region from amedical image including a heart region. The myocardium identifying unitis configured to identify a face of a myocardium region obtained byextending a face of the cardiac lumen region, identified by the cardiaclumen region identifying unit, by a certain distance toward a myocardiumside. The generating unit is configured to generate a color-coded imagein which the face of the myocardium region, identified by the myocardiumidentifying unit, is colored in colors according to signal values of themedical image corresponding to positions on the face of the myocardiumregion.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of the hardwareconfiguration of a medical imaging apparatus.

FIG. 2 is a flowchart describing the flow of a medical imaging processaccording to an embodiment of the present invention.

FIG. 3 is a diagram describing how a centroid of the aorta isidentified.

FIG. 4 is a diagram describing a central line generated by connectingthe centroid in each image.

FIGS. 5A to 5D are diagrams describing how a cardiac lumen region isextracted using a region growing method, starting from a cardiac apexside of the central line.

FIG. 6 is a diagram illustrating the relationship between changes involume of the cardiac lumen region extracted by the region growingmethod and time.

FIGS. 7A and 7B are diagrams describing a process of excluding anunnecessary region.

FIG. 8 is a diagram describing a process of excluding an unnecessaryregion.

FIG. 9 is a diagram illustrating a cardiac lumen region afterunnecessary regions have been excluded.

FIG. 10 is a diagram for describing a surface of the cardiac lumenregion and a face of a myocardium region.

FIG. 11 is a color-coded image of the face of the myocardium region.

FIG. 12 is a diagram describing a position for obtaining a threshold.

FIG. 13 is a diagram describing positions for obtaining a threshold.

FIG. 14 is a flowchart describing the flow of a medical imaging processaccording to an embodiment of the present invention.

FIG. 15A is an image of extracted coronary arteries and the like, andFIG. 15B is an image obtained by combining the image of extractedcoronary arteries and the like with a color-coded image of a virtualface.

FIG. 16 is an image obtained by combining the image of extractedcoronary arteries and the like with a color-coded image of a virtualface.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the following technique will be described in detail. Thistechnique generates an image to be provided for diagnosis of narrowingof coronary arteries by using one item of volume data (a plurality ofitems of slice image data) captured by a CT scanner in systole of apatient into which a radiocontrast agent has been injected.

A CT image captured by the CT scanner used in embodiments is an imageincluding a heart region, which is captured while a patient (subjectbeing tested), into which a radiocontrast agent has been injected viaintravenous drip or blood vessel injection, lies on a bed. Since aportion with a radiocontrast agent absorbs more X-rays, a high CT valueis obtained from this portion. By capturing a CT image in the aboveconditions, a CT image in which a cardiac lumen region where blood isflowing has high CT values is captured.

FIG. 1 is a diagram illustrating an example of the hardwareconfiguration of a medical imaging apparatus 101 according to theembodiments. The medical imaging apparatus 101 according to theembodiments is configured to obtain (load) volume data (a plurality ofmedical images) captured by a medical image diagnostic apparatus such asa CT scanner and stored in a storage device, and to perform imageprocessing.

A central processing unit (CPU) 201 integrally controls devices andcontrollers connected to a system bus 204.

A read-only memory (ROM) 202 or an external memory 211 (storage unit)stores the Basic Input/Output System (BIOS) and an operating systemprogram (hereinafter referred to as an OS), which are control programsfor the CPU 201, and various programs, which will be described later,necessary for implementing functions executed by the medical imagingapparatus 101. A random-access memory (RAM) 203 functions as a mainmemory, a work area, or the like for the CPU 201.

The CPU 201 is configured to load a program necessary in executingprocessing to the RAM 203, and to execute the program, therebyimplementing various operations.

An input controller (input C) 205 controls an input from an input device209 such as a keyboard, a pointing device such as a mouse (notillustrated), or the like.

A video controller (VC) 206 controls display on a display device such asa display 210. It is assumed that the type of display device is acathode-ray tube (CRT) or a liquid crystal display (LCD), but thedisplay device is not limited to these types.

A memory controller (MC) 207 controls access to the external memory 211such as a hard disk (HD), a flexible disk (FD), or a card memoryconnected via an adapter to a Personal Computer Memory CardInternational Association (PCMCIA) card slot, which stores a bootprogram, browser software, various applications, font data, user files,editing files, and various types of data.

A communication interface controller (communication I/F C) 208 isconfigured to connect and communicate with, via a network, an externaldevice such as a storage device that stores an image obtained by amedical image diagnostic apparatus such as a CT scanner, and executes acommunication control process through the network. For example, thecommunication I/F controller 208 is capable of performing communicationvia the Internet using the Transmission Control Protocol and InternetProtocol (TCP/IP).

Note that the CPU 201 is capable of performing display on the display210 by, for example, developing (rasterizing) an outline font onto adisplay information region in the RAM 203.

The CPU 201 also enables a user instruction to be given through a mousecursor (not illustrated) on the display 210.

Various programs and the like used to enable the medical imagingapparatus 101 according to the embodiments of the present invention toexecute later-described various processes are recorded in the externalmemory 211, and these programs are loaded as needed to the RAM 203,thereby enabling the CPU 201 to execute the programs.

Furthermore, definition files and various information tables used by aprogram according to the embodiments of the present invention are storedin the external memory 211.

First Embodiment

FIG. 2 is a flowchart describing the flow of a medical imaging processexecuted by the medical imaging apparatus 101 according to a firstembodiment of the present invention. The process illustrated in theflowchart of FIG. 2 is implemented by reading and executing a storedcontrol program by the CPU 201 of the medical imaging apparatus 101.

In S201 of FIG. 2, the CPU 201 of the medical imaging apparatus 101obtains, from a storage device (not illustrated), coronary vein CT imagedata obtained by a medical image diagnostic apparatus such as a CTscanner. The coronary vein CT image data obtained here is a plurality ofslice images constituting one item of volume data.

In S202, the CPU 201 of the medical imaging apparatus 101 identifies thecentroid of a high signal value region (region with high CT values) witha high degree of circularity in a slice image of the aorta side includedin the obtained CT image data. FIG. 3 illustrates the position of acentroid 301, identified in a slice image of the aorta side.Furthermore, similar identification operations are sequentiallyperformed, starting from the aorta side, on a plurality of slice imagesconstituting the volume data, until there remains no high signal valueregion, and the identified centroids are connected to extract a centralline. It can be said that a high signal value region with a high degreeof circularity is the aorta. By performing identification operations,starting from the aorta side, on slice images, a central line can becertainly identified as a pathway that extends from the aorta to acardiac apex 501 of the left ventricle, which causes an ischemicdisease. FIG. 4 illustrates by way of example a central line 401connecting the aorta, which is identified by connecting the centroids301 in the slice images as described above, and the cardiac apex 501 ofthe left ventricle. Note that the slice images used here include notonly slice images captured by a CT scanner, but also slice images thatare reconfigured from the volume data. Although the above examplediscusses the case where the central line is generated by connecting thecentroids 301 in the slice images, other methods may be used as long asthese methods are capable of extracting portions near the center of highsignal value regions.

In S203, the CPU 201 of the medical imaging apparatus 101 performs acardiac lumen region extracting process (region identification) using aregion growing method on the central line 401 extracted in S202,starting from the cardiac apex 501 side. The region glowing method is atechnique that can track a signal value on the basis of some sort ofindex from an arbitrary pixel (extraction start point). Using thistechnique, tracking is performed on the basis of the central line 401 asan index, starting from the cardiac apex 501 side, thereby extracting ahigh signal value region based on a radiocontrast agent. In doing so, acardiac lumen region ranging from the cardiac apex 501 of the leftventricle to the aorta and further toward the mitral valve can beextracted.

FIGS. 5A to 5D illustrate how extraction is performed using the regiongrowing method. FIGS. 5A and 5B illustrate states in which only acardiac lumen is extracted. FIG. 5C illustrates a state in which,besides the cardiac lumen region, an aorta 502 is started to beextracted. FIG. 5D illustrates a state in which extraction of thecardiac lumen region is almost completed, and extraction of a leftventricle 503 is started.

Extraction of the cardiac lumen region may be stopped at a time at whichthe cardiac lumen region has been sufficiently extracted. Since the sizeof the heart varies from one patient to another, the time to stopextraction is preferably determined by taking into consideration changesin the volume of the cardiac lumen region being extracted.

FIG. 6 is a diagram illustrating the relationship between the course oftime and changes in the volume of the extracted cardiac lumen regionusing the region growing method. As is clear from the diagram, thegrowth rate of the volume is substantially constant in a period of timein which only the cardiac lumen region is extracted. However, whenextraction of the aorta starts, the growth rate of the volume becomesfaster than before. Furthermore, when extraction of the left ventriclestarts, the growth rate of the volume becomes yet faster. In short, ifthe extraction process is stopped after the appearance of the secondinflection point of the growth rate of the volume, the cardiac lumenregion can be certainly extracted from any patient's heart images.Specifically, the extraction process is preferably controlled to bestopped at a time at which a certain amount of volume has been extractedor a certain period of time has elapsed after the appearance of thesecond inflection point.

Next, in S204, the CPU 201 of the medical imaging apparatus 101 performsa process of excluding an unnecessary region included in the cardiaclumen region extracted in S203. Note that the unnecessary regionexcluding process is preferably performed to improve the identifiabilityof an image, though this process is not an essential process.

As a specific process, as illustrated in FIG. 7A, a plane B connectingtwo coronary arteries 701 in the image, extracted in S203, isidentified. Thereafter, as illustrated in FIG. 7B, a plane B′ isidentified by translating in parallel the plane B by about 1 cm towardthe cardiac apex side. Since a region on the aorta side (upper side)with respect to the plane B′ is a region not to be used for diagnosis ofischemia, the region can be excluded. Furthermore, the same applies to aregion on the mitral valve side (left ventricle side), and a plane Calong with a left circumflex coronary artery 801 identified from theimage extracted in S203 is identified (FIG. 8). Since a region above theplane C is a region not to be used for diagnosis of ischemia, the regioncan be excluded.

In this manner, by identifying the plane B′ and the plane C andexcluding unnecessary regions, a three-dimensional color-coded imageincluding no unnecessary region can be obtained by performing a processof coloring different parts of the myocardium region in differentcolors. When this image is used by a doctor for diagnosis, whether anischemic region has been generated can be more easily identified. FIG. 9illustrates a cardiac lumen region identified by excluding unnecessaryregions from the cardiac lumen region extracted in S203.

In S205, the CPU 201 of the medical imaging apparatus 101 identifies asurface 1101 of the cardiac lumen region on the basis of the cardiaclumen region identified (cardiac lumen identification) by excludingunnecessary regions from the cardiac lumen region extracted in S203 inthis manner. Although the embodiment has discussed above the exemplarycase in which extraction is performed using the region growing method,other methods may be used as long as these methods can extract a cardiaclumen region.

In S206, the CPU 201 of the medical imaging apparatus 101 performs aprocess of extending the surface 1101 of the cardiac lumen region to amyocardium region including the endocardium. Specifically, the surfaceposition of the cardiac lumen region in each CT image is extended by afew pixels (a certain distance) at a time toward the myocardium side,and a position distant from the surface 1101 of the cardiac lumen regionby a certain amount (about 5 mm) is identified as a face 1102 (virtualface) of a myocardium region (myocardium identification). If thedistance extended here can be adjusted to an optimal distance, theposition becomes appropriate for early diagnosis of an ischemic lesion.Regarding how great the inward distance is from the surface 1101 of thecardiac lumen region, the setting is preferably changeable by the useraccordingly. It is not necessary to have the distance extended be equalin all regions, and the distance extended may be changed in accordancewith the region in the heart.

FIG. 10 illustrates a CT slice image including the surface 1101 of thecardiac lumen region, identified in S205, and the face 1102 of themyocardium region. As is clear from the image, each point of the surface1101 of the cardiac lumen region is displaced by a certain distance at atime along a straight line connecting the centroids 301, therebyidentifying the face 1102 of the myocardium region.

In S207, the CPU 201 of the medical imaging apparatus 101 performs aprocess of generating a three-dimensional image in which the face 1102of the myocardium region, identified in S206, is colored in accordancewith the level of a CT value according to each coordinate positionincluded in the face 1102. A color-coded image generated thereafter issaved in the external memory 211 of the medical imaging apparatus 101,for example, and is displayed on the display 210 or the like, therebyenabling the user such as a doctor to visually recognize the image.

The color coding method may have, for example, 100 as a presetthreshold. A CT value greater than or equal to 100 is colored in red,and a CT value less than 100 is colored in blue. Alternatively, stepwisethresholds are set, and the following color-coded image may begenerated. That is, a CT value greater than or equal to 110 is coloredin red; a CT value less than 110 and greater than or equal to 100 iscolored in orange; a CT value less than 100 and greater than or equal to90 is colored in green; a CT value less than 90 and greater than orequal to 80 is colored in blue; and a CT value less than 80 is coloredin black. Furthermore, a color-coded image may be generated not only bysetting a threshold(s), but also a color-coded image may be generatedusing gradations of color. FIG. 11 illustrates an example of an imagegenerated by performing such a color coding process on the face 1102 ofthe myocardium region. Here, a region 1103 with CT values that aregreater than or equal to 100, which is likely to be in a normal state,and a region 1104 with CT values that are less than 100, which is likelyto be in an ischemic state, are displayed in an identifiable manner.That is, differences in the signal level on the surface 1102 of themyocardium region are displayed in different colors, making it easy toidentify the state of the heart. Note that color coding according to theembodiment includes coloring of different parts in different color tonesby adjusting brightness or contrast.

By defining a preset threshold on the basis of a value obtained in anormal myocardium region, it is highly likely that an imagesubstantially suitable for determining narrowing of the coronaryarteries can be obtained. Therefore, a CT value at a position 1201 thatis exterior of the face 1102 of the myocardium region in one slice imageand that is within the range of the myocardium may be set as an initialthreshold value, as illustrated in FIG. 12, and a process of generatinga color-coded image may be performed on the basis of the set threshold.Furthermore, as illustrated in FIG. 13, CT values at a plurality ofpositions (1201 a to 1201 h) that are exterior of the face 1102 of themyocardium region and that are within the range of the myocardium may beobtained, an average of these CT values may be set as an initialthreshold value, and a process of generating a color-coded image may beperformed on the basis of the set threshold. In the case of obtaining CTvalues at a plurality of positions, in order to average the variations,CT values are preferably obtained at positions equidistant from thecentroid 301 of one slice image. Furthermore, CT values obtained notonly from one slice image, but also from a plurality of slice images maybe used.

Adjusting such a threshold to an optimal value can contribute to colorcoding for early diagnosis of an ischemic lesion. A preset threshold(initial value) is preferably made adjustable by the user appropriatelyby operating a tool bar or the like.

As described above, a face of a myocardium region is identified on thebasis of a cardiac lumen region, and on that face a color-coded imagebased on which the state of the left ventricular endocardium thatsensitively reacts to myocardial ischemia can be identified isgenerated, thereby providing an image that can contribute to reducingoversight of ischemic lesions. Furthermore, unlike a technique of therelated art, it is unnecessary to obtain a plurality of items of volumedata, and a three-dimensional color-coded image is generated from amedical image including a heart region that is one item of volume data,thereby reducing the amount of image data to be captured, and providingan image for diagnosis of narrowing of coronary arteries while reducingthe patient's exposure to radiation.

Second Embodiment

Although the first embodiment has discussed the exemplary case in whicha color-coded image based on which the state of the left ventricularendocardium can be identified is generated and displayed, not only theleft ventricular endocardium, but also the coronary arteries and thelike may be additionally displayed together. A second embodiment willdiscuss the exemplary case in which, besides the left ventricularendocardium, the coronary arteries are superimposed and displayed. Inthe second embodiment, points that are different from the firstembodiment will be mainly described, and descriptions of points that arethe same as the first embodiment will be omitted.

FIG. 14 is a flowchart describing the flow of a medical imaging processexecuted by the medical imaging apparatus 101 according to the secondembodiment. The process illustrated in the flowchart of FIG. 14 isimplemented by reading and executing a stored control program by the CPU201 of the medical imaging apparatus 101.

Since the processing in S1401 to S1407 of FIG. 14 is the same as theprocessing in S201 to S207 of FIG. 2, a description thereof will beomitted.

In S1408, the CPU 201 of the medical imaging apparatus 101 identifies,from the CT image obtained in S1401, coronary arteries for supplyingoxygen to the myocardium (coronary artery identifying unit). FIG. 15Aillustrates exemplary blood vessels such as coronary arteries identifiedas above. Here, a left coronary artery 1502 and a right coronary artery1503 branching off from an aorta 1501 are identified. Since suchcoronary arteries branch off from the root of the aorta, such coronaryarteries can be identified by extracting blood vessels that branch off.Note that this process of identifying coronary arteries may be performedin advance before a color-coded image is generated.

In S1409, the CPU 201 of the medical imaging apparatus 101 generates asuperimposed image by superimposing the coronary arteries identified inS1408 on a color-coded image generated according to CT values in S1407.Regarding the aorta side, it is preferable to identify portions near theposition of the plane B′ and the plane C identified in the process ofexcluding unnecessary regions in S1404, and to consecutively display thecoronary arteries, the aorta, and the color-coded image. Thereafter, thesuperimposed image is saved in the external memory 211 of the medicalimaging apparatus 101, for example, and is displayed on the display 210or the like, thereby enabling the user such as a doctor to visuallyrecognize the image.

FIG. 15B illustrates an example of an image obtained by combining imagesin S1409. By displaying the coronary arteries and the color-coded imagetogether as described above, which blood vessel is a coronary artery fordelivering blood to the region 1104 with CT values that are less than100, which is likely to be in an ischemic state, can be easilyidentified. That is, a blood vessel that is highly likely to have anarrowing can be easily identified. In the example illustrated in FIG.15B, it is clear that a first diagonal branch 1505 is positioned nearthe region 1104 which is highly likely to be in an ischemic state. Thus,the point that it is highly possible that there is a narrowing in thefirst diagonal branch 1505 can be easily identified.

Alternatively, a portion of the face of the myocardium region that hasCT values less than a preset threshold may be identified as the region1104 which is highly likely to be in an ischemic state, and further ablood vessel superimposed on the region 1104 (or a blood vessel near theregion 1104) may be identified. As illustrated in FIG. 16, the pathwayof the blood vessel may be emphasized by a broken line, for example, anddisplayed. Accordingly, the user such as a doctor can easily identifythe blood vessel which is highly likely to have a narrowing. By defininga preset threshold on the basis of a value obtained in a normalmyocardium region, as has been described in the first embodiment, it ishighly likely that a region substantially suitable for determiningnarrowing of the coronary arteries can be identified.

Although the embodiments have discussed above the example of using, as amedical image, a CT image captured by a CT scanner in systole of apatient into which a radiocontrast agent has been injected, a magneticresonance angiographic (MRA) image captured by a magnetic resonance (MR)scanner in systole may also be used.

The embodiments of the present invention include embodiments as, forexample, a system, an apparatus, a method, a program, or a storagemedium. Specifically, the embodiments of the present invention may beapplied to a system including a plurality of devices, or may be appliedto an apparatus including only one device. Note that the embodiments ofthe present invention include a software program implementing thefunctions of the above-described embodiments, which is directly suppliedto a system or an apparatus, or which is supplied from a remote place.The embodiments of the present invention also include the system or theapparatus which reads and executes the supplied program code toimplement the functions.

Therefore, program code itself to be supplied to and installed in aninformation processing apparatus in order to implement, on theinformation processing apparatus, the functions and processes accordingto the above-described embodiments also implements the presentinvention. In other words, a computer program itself for implementingthe above-mentioned functions and processes is also included in theembodiments of the present invention.

In that case, such a program may have any form such as object code, aprogram executed by an interpreter, or script data supplied to an OS, asfar as it functions as a program.

Examples of recording media for supplying a program include a flexibledisk, a hard disk, an optical disk, a magneto-optical disk (MO), acompact-disc read-only memory (CD-ROM), a compact-disc recordable(CD-R), and a compact-disc rewritable (CD-RW). Other examples include amagnetic tape, a non-volatile memory card, a ROM, and a digitalversatile disc (DVD including DVD-ROM and DVD-R).

Moreover, one method of supplying a program includes connecting to ahomepage on the Internet by using a browser on a client computer. Acomputer program according to the embodiments of the present inventioncan be supplied by downloading the computer program itself from thehomepage or by downloading a file including the compressed computerprogram with an auto-install function to a recording medium such as ahard disk.

Program code configuring a program according to the embodiments of thepresent invention can be divided into a plurality of files, and thesefiles can be downloaded from different homepages, thereby implementingthe above-described functions and processes. In other words, a WorldWide Web (WWW) server that enables a plurality of users to download aprogram file for implementing, with an information processing apparatus,the functions and processes according to the embodiments of the presentinvention is also included in the embodiments of the present invention.

A program according to the embodiments of the present invention may beencrypted, stored on a storage medium such as a CD-ROM, and distributedto a user. A user who satisfies a certain condition may be allowed todownload key information for decrypting the encryption from a homepagevia the Internet. Using the downloaded key information, the user maydecrypt the encrypted program and install the decrypted program in aninformation processing apparatus, thereby implementing the functions andprocesses.

Alternatively, the functions of the above-described embodiments areimplemented by an information processing apparatus that executes aprogram that has been read. Moreover, on the basis of an instruction ofthe program, an OS running on the information processing apparatus, forexample, may perform the entirety or part of the actual processing, andthat processing may implement the functions of the above-describedembodiments.

Furthermore, a program read out from a recording medium is written on amemory included in a feature expansion board inserted in an informationprocessing apparatus or a feature expansion unit connected to aninformation processing apparatus. Thereafter, on the basis of aninstruction of the program, a CPU included in the feature expansionboard or the feature expansion unit performs the entirety or part of theactual processing, and that processing implements the functions of theabove-described embodiments.

Note that the above-described embodiments are merely examples of theembodiments of the present invention, and the technical scope of thepresent invention is not construed to be restrictively interpreted bythese embodiments. That is, the present invention can be implemented invarious forms without departing from the technical spirit or majorfeatures of the present invention.

According to the above-described embodiments, an image provided fordiagnosis of narrowing of coronary arteries can be generated by using amedical image captured in systole. By identifying a face of a myocardiumregion using a cardiac lumen region and displaying that face in colorsaccording to signal values of a medical image at positions on the face,an image provided for diagnosis of narrowing of coronary arteries can beprovided by using only a medical image including a heart region that isone item of volume data.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2014-209259, filed Oct. 10, 2014, and Japanese Patent Application No.2015-131597, filed Jun. 30, 2015, which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. A medical imaging apparatus comprising: a cardiaclumen region identifying unit configured to identify, based on signalvalues of a region where blood is flowing, a cardiac lumen region from amedical image including a heart region; a myocardium identifying unitconfigured to identify a face of a myocardium region obtained byextending a surface of the cardiac lumen region, identified by thecardiac lumen region identifying unit, by a certain distance at a timetoward a myocardium side; and a generating unit configured to generate athree-dimensional color-coded image in which the face of the myocardiumregion, identified by the myocardium identifying unit, is colored incolors according to signal values of the medical image corresponding topositions on the face of the myocardium region.
 2. The medical imagingapparatus according to claim 1, wherein the cardiac lumen regionidentifying unit includes an extracting unit configured to extract aline connecting an aorta and a cardiac apex of a left ventricle by usingthe medical image, and a region identifying unit configured to regardthe cardiac apex side of the line extracted by the extracting unit as astarting point and to identify the cardiac lumen region using a regiongrowing method.
 3. The medical imaging apparatus according to claim 2,wherein the region identifying unit identifies the cardiac lumen regionafter excluding an unnecessary region.
 4. The medical imaging apparatusaccording to claim 1, wherein the generating unit generates an imagebased on which a level difference is identifiable, by coloring the imagein different colors on the basis of a threshold.
 5. The medical imagingapparatus according to claim 4, wherein the threshold is provided insteps, and the image is colored in different colors in accordance withthese steps to enable displaying of the image so that a level differenceis identifiable.
 6. The medical imaging apparatus according to claim 4,wherein the threshold is determined using a signal value obtained in anormal myocardium region.
 7. The medical imaging apparatus according toclaim 1, wherein the cardiac lumen region identifying unit identifies aregion including left ventricular endocardium.
 8. The medical imagingapparatus according to claim 1, further comprising: a coronary arteryidentifying unit configured to identify a coronary artery, wherein thegenerating unit generates a superimposed image by superimposing thecoronary artery identified by the coronary artery identifying unit onthe color-coded image.
 9. The medical imaging apparatus according toclaim 8, further comprising: a region identifying unit configured toidentify, out of the face of the myocardium region, a region with asignal value that is less than a certain threshold, wherein thegenerating unit generates the superimposed image so that a blood vesselsuperimposed on the region identified by the region identifying unit ora blood vessel near the region becomes identifiable.
 10. The medicalimaging apparatus according to claim 1, wherein the medical imageincluding the heart region is one item of volume data captured insystole.
 11. The medical imaging apparatus according to claim 1, whereinthe medical image including the heart region is a computed tomographicimage or a magnetic resonance angiographic image.
 12. A non-transitorycomputer-readable recording medium having stored thereon a program forcausing a computer to perform a medical imaging method, the medicalimaging method comprising: a cardiac lumen region identifying step ofidentifying, based on signal values of a region where blood is flowing,a cardiac lumen region from a medical image including a heart region; amyocardium identifying step of identifying a face of a myocardium regionobtained by extending a surface of the cardiac lumen region, identifiedin the cardiac lumen region identifying step, by a certain distance at atime toward a myocardium side; and a generating step of generating athree-dimensional color-coded image in which the face of the myocardiumregion, identified in the myocardium identifying step, is colored incolors according to signal values of the medical image corresponding topositions on the face of the myocardium region.
 13. A medical imagingmethod comprising: a cardiac lumen region identifying step ofidentifying, based on signal values of a region where blood is flowing,a cardiac lumen region from a medical image including a heart region; amyocardium identifying step of identifying a face of a myocardium regionobtained by extending a surface of the cardiac lumen region, identifiedin the cardiac lumen region identifying step, by a certain distance at atime toward a myocardium side; and a generating step of generating athree-dimensional color-coded image in which the face of the myocardiumregion, identified in the myocardium identifying step, is colored incolors according to signal values of the medical image corresponding topositions on the face of the myocardium region.
 14. A medical imagingapparatus comprising: a central processing unit; a memory storing aprogram including a group of instructions for causing the centralprocessing unit to execute a process, the process including: a firstprocess of identifying, based on signal values of a region where bloodis flowing, a cardiac lumen region from a medical image including aheart region; a second process of identifying a face of a myocardiumregion obtained by extending a surface of the cardiac lumen region,identified by the first process, by a certain distance toward amyocardium side; and a third process of generating a three-dimensionalcolor-coded image in which the face of the myocardium region, identifiedby the second process, is colored in colors according to signal valuesof the medical image corresponding to positions on the face of themyocardium region.
 15. A medical imaging system comprising: a cardiaclumen region identifying unit configured to identify, based on signalvalues of a region where blood is flowing, a cardiac lumen region from amedical image including a heart region; a myocardium identifying unitconfigured to identify a face of a myocardium region obtained byextending a surface of the cardiac lumen region, identified by thecardiac lumen region identifying unit, by a certain distance at a timetoward a myocardium side; and a generating unit configured to generate athree-dimensional color-coded image in which the face of the myocardiumregion, identified by the myocardium identifying unit, is colored incolors according to signal values of the medical image corresponding topositions on the face of the myocardium region.
 16. A medical imagingapparatus comprising: a cardiac lumen region identifying unit configuredto identify a cardiac lumen region from a medical image including aheart region; a myocardium identifying unit configured to identify aface of a myocardium region obtained by extending a surface of thecardiac lumen region, identified by the cardiac lumen region identifyingunit, by a certain distance at a time toward a myocardium side; agenerating unit configured to generate a color-coded image in which theface of the myocardium region, identified by the myocardium identifyingunit, is colored in colors according to signal values of the medicalimage corresponding to positions on the face of the myocardium region,and a coronary artery identifying unit configured to identify a coronaryartery, wherein the generating unit generates a superimposed image bysuperimposing the coronary artery identified by the coronary arteryidentifying unit on the color-coded image.
 17. The medical imagingapparatus according to claim 16, further comprising: a regionidentifying unit configured to identify, out of the face of themyocardium region, a region with a signal value that is less than acertain threshold, wherein the generating unit generates thesuperimposed image so that a blood vessel superimposed on the regionidentified by the region identifying unit or a blood vessel near theregion becomes identifiable.